                       possible-ctx
                       (make-context (objects certain-ctx)
                                     (attributes certain-ctx)
-                                    (set-of [g m] | g (objects certain-ctx)
-                                                    m (close-under-implications
-                                                       new-implications
-                                                       (oprime certain-ctx #{g})))))))))))))
+                                    (set-of [g m] [g (objects certain-ctx),
+                                                   m (close-under-implications
+                                                      new-implications
+                                                      (oprime certain-ctx #{g}))])))))))))))
 
 ;;;
 

                                           (set-of [g m] [[g pos _] counterexamples,
                                                          m pos])))))
             ;;
             true                       ; add implication
             (let [new-implications (conj implications new-impl)]
               (recur new-implications
                      (next-closed-set (attributes possible-ctx)

  to construct a special handler using the «make-handler»
  function. See the corresponding documentation of «make-handler»."
  [possible-ctx, certain-ctx,
   & {:keys [background-knowledge handler]
      :or   {:background-knowledge #{},
             :handler default-handler-for-incomplete-counterexamples}}]
  (println background-knowledge handler)
  (assert (set? background-knowledge))
  (assert (= (attributes certain-ctx)
             (attributes possible-ctx))
